The present invention relates to actuators for use with variable valve mechanisms of internal combustion engines.
A variable valve mechanism controls the valve lift profile (i.e., the amount and duration of lift) of one or more associated valves of an engine in response to engine operating parameters, such as, for example, engine load, speed, and driver input. Generally, the valve lift profile is set by an actuator which, varies the angular position of a control shaft which, in turn, varies the angular position of the variable valve mechanism relative to a central axis of an input shaft or camshaft of the engine to which the variable valve mechanism is pivotally mounted.
Actuators for variable valve mechanisms typically include a motor and gearbox. One example of an actuator for a variable valve mechanism is described in commonly-assigned U.S. Pat. No. 6,019,076, the disclosure of which is incorporated herein by reference. The gearbox includes a worm which engages a worm gear disposed on or connected to the control shaft. When a change in the valve lift profile is desired, the motor rotates the worm which, in turn, rotates the worm gear. Rotation of the worm gear pivots the control shaft relative to its central axis which, in turn, angularly positions the variable valve mechanism relative to the central axis of the camshaft to thereby establish a desired valve lift profile.
The input or camshaft of the engine is driven by the engine and rotates three-hundred sixty degrees. As stated herein, the variable valve mechanism is pivotally mounted on an input shaft or camshaft of the engine. The variable valve mechanism is subjected to torque as a result of the rotation of the camshaft or input shaft to which it is pivotally mounted. This torque is reflected from the variable valve mechanism through the control shaft and back to the actuator. A spring acts upon the worm gear and/or the control shaft to substantially equalize the positive and negative peaks of the reflected torque to which the control shaft and actuator are subjected. In the static state, i.e., when the control shaft is stationary, the pressure and lead angles of the teeth of the worm and worm gear are designed such that torque reflected from the variable valve mechanism through the control shaft causes the worm and the worm gear to lock up. The locking of the worm and worm gear in the static state prevent the reflected torque from being transmitted to the motor. However, in order to pivot the control shaft, the motor must be adequately powered to unlock the worm and worm gear and to overcome the reflected torque.
During pivoting of the control shaft, the worm and worm gear are no longer locked up. Thus, the motor is subjected to the reflected torque peaks. The reflected torque peaks may reach a large enough magnitude and, if directed opposite to the direction of motor rotation, cause the worm and worm gear to lock up and the motor to stall. The motor will remain stalled until the momentary torques decrease and the motor is again able to drive the mechanism in the desired direction.
Such conventional actuators require numerous parts, complicated control means, and lash adjustment systems to compensate for tolerances in manufacturing, temperature changes, and wear. The motor and gearbox must be relatively large and powerful in order to overcome the reflected torque peaks, and thus consume a substantial amount of space. An overpowered motor is relatively expensive and heavy.
Therefore, what is needed in the art is an actuator for variable valve mechanisms that has fewer parts and is less costly to manufacture.
Furthermore, what is needed in the art is an actuator for variable valve mechanisms that requires no lash adjustment system.
Still further, what is needed in the art is an actuator for variable valve mechanisms that is less sensitive to and less affected by reflected torque.
The present invention provides an actuator for use with variable valve mechanisms of internal combustion engines.
The invention comprises, in one form thereof, a cylinder having a central axis and a side wall. The side wall has an inner surface. A clutch is disposed within the cylinder, and includes a hub and at least one clutch arm. Each clutch arm includes a negative opposing finger, a positive opposing finger, a negative opposing spring and a positive opposing spring. The negative opposing finger has a first end attached to the hub and a fingertip end engaging the inner surface of the side wall. The positive opposing finger has a first end attached to the hub and a fingertip end engaging the inner surface of the side wall. The negative opposing spring has a first end attached to the negative opposing finger. The positive opposing spring has a first end attached to the positive opposing finger. A control input is disposed within said cylinder, and is configured for engaging a second end of a selected one of the negative opposing spring and the positive opposing spring.
An advantage of the present invention is that a simpler and less expensive gear box can be used since torque peaks from the control shaft are substantially absorbed by the clutch.
Another advantage of the present invention is that it requires no lash adjustment system.
A still further advantage of the present invention is that it consumes less space and is lighter in weight than conventional actuators.